1. Field of the Invention
This invention is related to multimedia packet networks. Specifically, this invention relates to a mechanism to allow a call server to control the operation of a programmable phone, which is connected to a media gateway within such a network.
2. Description of the Problem
Evolution of the public switched telephone network (PSTN) has accelerated in recent years; however, most of the PSTN still operates on circuit switched, time division multiplexed (TDM) connections. Integrated services digital network (ISDN) bearer channels often provide transport. In parallel with the PSTN, a packet based data network has evolved. This data network has largely been used for Internet traffic and data networking. Although these networks have been mostly separate until recently, the two networks are starting to merge. The merger of these networks requires that voice traffic be carried over packet networks, and further that such packet networks be able to seamlessly integrate with traditional circuit switched networks, as the two types of networks may carry different call legs of the same call.
FIG. 1 is a block diagram of the hardware that connects a telephone into the PSTN to provide calling functions. A service control module (SCM), 101, controls the function of the switching system of a central office. The central office provides access to the public switched telephone network (PSTN), 105, for a telephone, 102. The telephone in this case is a “plain old telephone system” (POTS) analog phone. Peripheral module (PM) 106 contains a local call signaling processing function, 103, and a circuit switching function, 104, which handle voice and other signals being exchanged with the POTS phone, 102. Calls may pass through multiple toll offices, may be connected directly from one end office to another, or may be switched within the same end office. Signaling between offices is typically provided by an ISUP (ISDN user part) connection through other peripheral modules. ISUP signaling is well understood and is standard in the telecommunications industry. For more information on ISUP signaling, see the various International Telecommunications Union (ITU) Recommendations pertaining to telephone signaling, including Q.761, Q.764 and Q.931, the most recent versions of which at the time of filing this application are incorporated herein by reference.
FIG. 2 is a block diagram of the hardware used to connect a telephone to a packet switched network. In the case of FIG. 2, a telephone or other legacy device or network connected to the media gateway is said to be connected at an “endpoint” of the packet network. The call is transported from one end office to another via a packet switched network 205. In most cases the packet network is an asynchronous transfer mode (ATM) network or an internet protocol (IP) network, but frame relay (FR) or other network types can be used. The fact that the call traverses a packet network is, in theory, transparent to a caller using POTS telephone 202. In order for the packet network to seamlessly connect with devices or equipment at an endpoint, like POTS telephones, designed for the PSTN, one type of media must be converted to another. This conversion is referred to generally as voice packetization. In the ATM case it is also sometimes referred to as circuit emulation services (CES). The device that provides this conversion is called a media gateway (MG), 204 in FIG. 2. In the system of FIG. 2, a media gateway handles each end of a bearer connection through packet network 205. The media gateway and the packet network it serves may be capable of processing audio and video. The media gateway is capable of full duplex media translations. It may also provide other features such as conferencing.
Each media gateway is associated with a media gateway controller (MGC), 203 of FIG. 2. The media gateway is “dumb” in that it does not have call processing capabilities. The call processing capabilities for the network reside in the MGC, 203, and in its SCM, 201. The MGC and the SCM are together referred to as a “call server” (CS), 206. A call server provides the services interaction and controls the call state of a media gateway. The protocol used by the MGC portion of the call server to control the MG is called the media gateway control protocol (MGCP), for example, the so-called “Megaco” protocol. Megaco is an application layer protocol which is also described in ITU Recommendation H.248, which shares a common text with the Internet Engineering Task Force (IETF) Internet Draft “Megaco Protocol,” and which is incorporated herein by reference. The “Megaco Protocol” was derived from an MGCP Internet Draft but was renamed “Megaco” and became an IETF working document in March, 1999. Throughout the rest of this disclosure we will refer to Megaco as “Megaco/H.248.”
The architecture described above and shown in FIG. 2 has been widely published and accepted. However, it is still under development and has seen little deployment. There are still problems to be overcome before such networks can serve all users with the same features that such users have come to expect from the PSTN. One problem is that the Megaco/H.248 protocol provides limited signaling for control of customer premises equipment (CPE) functions. The protocol was designed to recognize only the basic functions of POTS telephones; yet there is a huge myriad of other types of programmable, digital and analog phones, as well as other devices, available and in use. In the PSTN, programmable phones rely on signals exchanged with the switch or some other type of central call control to implement lamps, function keys, screen displays, etc. In addition to standard programmable phones, such as ISDN and analog display services interface (ADSI) phones, there are many types of standard or manufacturer specific programmable phones that use or can use non-standard, manufacturer specific signaling to perform these functions. Some non-standard programmable phones are sometimes generically called “P-phones.” Because there are a number of possible types of programmable phones, it is impossible to include signaling for all of them in Megaco/H.248. What is needed is a way for a call server or MGC to control these functions of a programmable phone without adding new, telephone specific signaling to the standard Megaco/H.248 protocol.